mov dx, seg DTA
mov ds, dx
mov dx, offset DTA ;ds:dx is new disk transfer address
mov ah, 1Ah ;Set Disk Transfer Address
int 21h
Set Disk Transfer Address (Function 1Ah) sets the address of the buffer MS-DOS uses for file I/O (with file control blocks, or FCBs) and disk searches (with and without FCBs).
DTA
Points to the buffer MS-DOS is to use for file operations.
This function has no return value.
When a program starts, the default disk transfer address (DTA) is offset 0080h in the program segment prefix (PSP). If a program sets the DTA, the new buffer must be large enough to accommodate the file record size (for example, if the file record size is 128 bytes, the buffer must be at least 128 bytes). In addition, the buffer must not overlap a segment boundary. The default DTA should not be used for read or write operations with record sizes that exceed 128 bytes.
Programs can retrieve the current DTA with Get Disk Transfer Address (Function 2Fh).
Function 11h Find First File with FCB
Function 12h Find Next File with FCB
Function 14h Sequential Read
Function 15h Sequential Write
Function 21h Random Read
Function 22h Random Write
Function 27h Random Block Read
Function 28h Random Block Write
Function 2Fh Get Disk Transfer Address
Function 4Eh Find First File
Function 4Fh Find Next File